/*
 * Copyright 2021 Shulie Technology, Co.Ltd
 * Email: shulie@shulie.io
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.shulie.surge.data.runtime.disruptor;

import java.util.concurrent.atomic.AtomicBoolean;

/**
 * No operation version of a {@link EventProcessor} that simply tracks a {@link Sequence}.
 *
 * This is useful in tests or for pre-filling a {@link RingBuffer} from a publisher.
 */
public final class NoOpEventProcessor implements EventProcessor
{
	private final SequencerFollowingSequence sequence;
	private final AtomicBoolean running = new AtomicBoolean(false);

	/**
	 * Construct a {@link EventProcessor} that simply tracks a {@link Sequence} object.
	 *
	 * @param sequencer to track.
	 */
	public NoOpEventProcessor(final RingBuffer<?> sequencer)
	{
		sequence = new SequencerFollowingSequence(sequencer);
	}

	@Override
	public Sequence getSequence()
	{
		return sequence;
	}

	@Override
	public void halt()
	{
		running.set(false);
	}

	@Override
	public boolean isRunning()
	{
		return running.get();
	}

	@Override
	public void run()
	{
		if (!running.compareAndSet(false, true))
		{
			throw new IllegalStateException("Thread is already running");
		}
	}

	/**
	 * Sequence that follows (by wrapping) another sequence
	 */
	private static final class SequencerFollowingSequence extends Sequence
	{
		private final RingBuffer<?> sequencer;

		private SequencerFollowingSequence(final RingBuffer<?> sequencer)
		{
			super(Sequencer.INITIAL_CURSOR_VALUE);
			this.sequencer = sequencer;
		}

		@Override
		public long get()
		{
			return sequencer.getCursor();
		}
	}
}
